eljobso eljobso - 2 months ago 9
Python Question

Get intersection of list elements with different sublist datatypes

I have two lists, which contains list elements, e.g:

list1 = [['placeholder1', {'data': 'data1'}], ['placeholder2', {'data': 'data2'}], ['placeholder2', {'data': 'data1'}]]
list2 = [['placeholder2', {'data': 'data2'}], ['placeholder3', {'data': 'data5'}]]

intersection_result = [['placeholder2', {'data': 'data2'}]]


The structure of the sub-list elements is just an example. It can also happen that all the sub-list elements contains strings
['asdf', 'qwert']
or a mixture of string and numbers
['sdfs', 232]
. However, the sub-list structure is always the same (in both lists).

How can I get the intersection of lists elements which are identical in both lists?

Jim Jim
Answer

If my understanding is correct, you can get the intersection by checking and selecting any() of the elements in the smallest list which are equal to ones in the larger one.

With a comprehension, this would look like this:

intersection_res = [l for l in min(list2, list1, key=len) if any(l == l2 for l2 in max(list1, list2, key=len))]

This uses, min and max with a key assigned to len to always select from the smaller list and check against the larger one.

This yields:

print(intersection_res)
[['placeholder2', {'data': 'data2'}]]

This comprehension can be trimmed down if you pre-assign the min-max lists or, of course, if you are always certain which list is larger than the other:

sm, la = list1, list2 if len(list1) < len(list2) else list2, list1
intersection_res = [l for l in sm if any(l == l2 for l2 in la)]
Comments